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Hey, guys, I'm back with another tough question. I have three AC outlets in the room. The room has only 1 three-prong outlet into which my UPS is plugged. My UPS has my computer and monitor plugged into it. Whenever I plug a motorized device (microwave, hairdryer or portable heater) into either of the other two outlets and turn it on, the image on my CRT monitor violently shakes until I turn off the motorized device.

The cause can't be EMI because the monitor image is stable when those same motorized devices are plugged into an outlet in a different room, turned on using a super long heavy-duty extension cord, and placed the same distance from the monitor in the room with my computer.

The UPS never switches to battery while the monitor image violently shakes, so the problem must not be causing an undervoltage or overvoltage that could damage the motherboard, specifically the VGA port and onboard VRAM, right? What do you suppose is the cause?

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The cause can't be EMI because the monitor image is stable when those same motorized devices are plugged into an outlet in a different room

Well, if the power cable (main arrival) passes just next to the screen, it's still likely to be. Because in the 1st case the stronger power goes through that cable, in the 2nd case it does not. Solution is to pull the CRT away from the wall.

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The cause can't be EMI because the monitor image is stable when those same motorized devices are plugged into an outlet in a different room

Well, if the power cable (main arrival) passes just next to the screen, it's still likely to be. Because in the 1st case the stronger power goes through that cable, in the 2nd case it does not. Solution is to pull the CRT away from the wall.

The power cable of a motorized device? If so, the power cable is plugged into an outlet on the left or right side of the room and not close to the monitor. And when a motorized device is plugged into an outlet in the other room, the extension cord is closer to the monitor but does not cause the monitor image to shake.

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The issue seems to be that you have one or more "large appliances" on the same house circuit as the computer. A UPS that doubles as a power line conditioner should help. A PC power supply with active power factor conversion should also help to reduce fluctuations on the AC line.

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No, I was talking about the MAIN cable that brings power to "the outlet on the left or right side of the room". It is possible that that cable is placed in a way that it creates interferences with the magnetic fields of your screen. Maybe you can't see that cable but it has to be somewhere.

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The issue seems to be that you have one or more "large appliances" on the same house circuit as the computer. A UPS that doubles as a power line conditioner should help. A PC power supply with active power factor conversion should also help to reduce fluctuations on the AC line.

I know the problem is the two outlets. I just didn't know what the problem was. That sounds right because if the toaster oven is plugged into the kitchen outlet and air-conditioner is plugged into the living room outlet and both are turned on, it causes a blackout, so this must be the same deal on another line.

My only concern is if I forget not to plug a motorized device into one of the two outlets, could this damage my motherboard? The monitor is still working. I want to say no because the computer and monitor are connected to a high-quality UPS that never switches to battery when it looks like the monitor is having a brownout, sag, spike or surge, but there could be something else to it.

I only use PFC power supplies and I don't think a line-conditioning UPS would detect the brownout, sag, spike or surge because this standby UPS never does.

Edited January 12, 2012 by vipejc

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No, I was talking about the MAIN cable that brings power to "the outlet on the left or right side of the room". It is possible that that cable is placed in a way that it creates interferences with the magnetic fields of your screen. Maybe you can't see that cable but it has to be somewhere.

A good theory. I'm just gonna write two notes and tape them above both problematic outlets that reads: Do NOT plug a motorized or large device into this outlet. Doing so could damage the computer.

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To determine if your problem is dirty power or EMI you could try a very simple test. Unplug the UPS from the wall with the computer and monitor on so they run off the battery. Plug your hairdryer into the wall by your computer and turn it on. If the monitor image shakes then the problem is EMI. If it doesn't then you need to move the PC to another AC circuit in the house, or use an "always on" power conditioner.

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To determine if your problem is dirty power or EMI you could try a very simple test. Unplug the UPS from the wall with the computer and monitor on so they run off the battery. Plug your hairdryer into the wall by your computer and turn it on. If the monitor image shakes then the problem is EMI. If it doesn't then you need to move the PC to another AC circuit in the house, or use an "always on" power conditioner.

That's a great suggestion. And correction, the monitor image shakes only when a motorized device that uses a lot of watts is plugged into either of the two outlets. The TV, Xbox and Xbox 360 do not cause the monitor image to shake, because they do not have motors.

Can dirty power or EMI cause hardware damage to a computer that is connected to a UPS that never detects a power problem?

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Xbox and Xbox 360 do not cause the monitor image to shake, because they do not have motors.

Sure they do! I'd hope that these fine products have fans in them, also there would be a "motor" in the hard drive and optical drives too.

You can do some extra testing to see where the problem is. Try having just the monitor connected to that outlet (sans UPS) and try connecting one of these appliances and see if the problem still occurs. Then (with the use of a 3 prong adapter) I would plug the monitor into one of the other outlets, and try an appliance in both the other 2 prong AND in the 3 prong plug to see if the same thing still happens.

Then you'd want to know if all three outlets are on the same circuit, or if the outlet you mentioned that didn't cause the problem is on the same or different circuit.

FWIW, having 1 3 prong outlet and 2 in the same room (aka lack of grounding on the 2 prongs) shouldn't cause this type of problem... even while it is entirely possible that the 3 prong outlet isn't grounded either. People who build/work on houses do strange things.

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Xbox and Xbox 360 do not cause the monitor image to shake, because they do not have motors.

Sure they do! I'd hope that these fine products have fans in them, also there would be a "motor" in the hard drive and optical drives too.

You can do some extra testing to see where the problem is. Try having just the monitor connected to that outlet (sans UPS) and try connecting one of these appliances and see if the problem still occurs. Then (with the use of a 3 prong adapter) I would plug the monitor into one of the other outlets, and try an appliance in both the other 2 prong AND in the 3 prong plug to see if the same thing still happens.

Then you'd want to know if all three outlets are on the same circuit, or if the outlet you mentioned that didn't cause the problem is on the same or different circuit.

FWIW, having 1 3 prong outlet and 2 in the same room (aka lack of grounding on the 2 prongs) shouldn't cause this type of problem... even while it is entirely possible that the 3 prong outlet isn't grounded either. People who build/work on houses do strange things.

But why isn't the UPS detecting the undervoltage? And is my hardware being slowly damaged every time I forget not to plug in a high-watt device into one of the two outlets, which is rarely and the device is on for no longer than an hour when I do forget.

The UPS came with a good connected-equipment warranty and I was assured by the company my equipment is being protected, but if it's an undervoltage, I'm not so sure.

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Post #6 suggests that you have a "draw" of current (two large munching devices on simultaneously) indicating low power (for want of a better term) being supplied, further drawing from the PC (probably in the same line as already suggested). The suggestion that 2-prong vs 3-prong is ok UNLESS you have two wires "swapped" - this is a common cause of "hum" in a P.A. system connected to incorrectly wired (common reduction of "hum" is a "ground lift" or not using the "ground") outlets. Sounds like your house wiring is a bit kludged... Check the gauge of wires, check the fuse/breaker amperage (don't go over the allowable for said gauge), get a "tester" (about $10) at radio shack - 3 lights on it and plugs into a 3-prong plug. Use an "adapter" (3->2 prong "ground lift") with it to test the non-grounded plugs. There may be many "reversed" wires in the outlets (bad ju-ju) that we avoid when gigging for that very "hum" problem that refuses to go away. The "tester" will show you what's wrong (just the lights, folks). Fix those items and many/most problems will go away all over the place. Ensure that fuse/breaker is OFF before fiddling with (and you are probably doing something the city inspector and unions would frown upon).

Bottom line, all of the above posts (plus mine) indicates you may have one or more electrical problems.

edit - lastly... CHEAT and put another fuse/breaker into the mains and run a spanky new wire/outlet (call it an "extension) to your "pc room", bypassing the rest of the house... ("DANGER, Will Robinson!")